Both crystalline and amorphous polyolefins are known. In particular, both crystalline and amorphous polypropylenes have been disclosed. Typical amorphous polypropylenes may be gummy materials of little strength. Highly crystalline polypropylenes may provide strength, but are generally not elastic.
Rubbery polypropylenes are also known. Such products may be produced directly by conventional polymerization using particular catalysts, by repeated extractions of conventional polypropylene, by chemical treatment of crystalline polypropylene, and/or by sequential polymerization processes. Representative rubbery polypropylenes are described in U.S. Pat. No. 3,329,741 to Schrage et al., U.S. Pat. No. 3,175,999 to Natta et al., U.S. Pat. No. 3,511,824 to Listner and U.S. Pat. No. 3,784,502 to Gobran et al. Other references directed to polyolefins having elastic character include the following:
U.S. Pat. No. 4,826,939 to Stuart is directed to a highly amorphous propylene-based olefin terpolymer made by a process wherein ethylene is very randomly incorporated into a chain along with propylene and hexene. The amorphous terpolymer of Stuart is very tacky and pressure sensitive, having a ring and ball softening point of about 75 to 120° C. The process of making the disclosed amorphous terpolymer comprises polymerizing the monomers in the presence of a traditional anionic coordination catalyst within a temperature range typical of a solution polymerization processes, about 140 to 250° C. However, these materials lack elastic character.
U.S. Pat. No. 4,335,225 to Collette et al. is directed to a semicrystalline or crystalline block polypropylene having excellent elastomeric properties, which can be made with the use of particular titanium, zirconium, or hafnium-based catalyst systems. However, Collette discloses very low yields in a slurry process. Also, the use of these catalysts requires very mild processing conditions because the catalysts are particularly sensitive to air, heat, and light. Accordingly, the teachings of Collette are not suitable nor readily adaptable to a solution process.
U.S. Pat. No. 6,084,047 to Holliday et al. is directed to an elastomeric polyolefin terpolymer comprising about 5 to 25 weight percent ethylene units, from greater than about 5 to about 40 weight percent hexene units, and about 35 to less than about 90 weight percent propylene units, wherein the total weight percent of monomer units equals 100 percent. The polyolefin terpolymer has a melt flow rate of about 0.01 to 500 grams per 10 minutes and a tensile set of about 65 to 120 percent, according to ASTM D-412.
U.S. Patent Application Publication No. US2003/0083434 A1 to Ouhadi et al. is directed to adhesive compositions comprising a thermoplastic elastomer and a block copolymer with rigid vinyl aromatic blocks and non-rigid blocks of dienes and vinyl aromatic monomers. Ouhadi does not disclose polypropylene based resins, but instead is directed to a dispersed phase within an at least partially vulcanized (crosslinked) rubber component.
Veghini et al. (Veghini, D.; Henling, M.; Burkhardt, T; Bercaw, J. J. Am. Chem. Soc. 1999, 121, 564-573) which is incorporated by reference herein disclose various catalysts which may produce syndiotactic polypropylene, yet the reference does not disclose resultant polymers having both high impact strength and high elasticity.
Rieger et al., (Rieger, B.; Troll, C.; Macromolecules 2002, 35, 5742-5743) is directed to so called ultra high molecular weight polypropylene elastomers produced using dual side hafnocene catalysts. In Rieger, the molecular weights range between 700,000 and 5,000,000, resulting in semi-crystalline polymers having only slight elastomeric properties. In fact, Rieger notes that thermoplastic polyolefins of low crystallinity suffer from high set values in stress-strain hysteresis testing.
Numerous references are directed to compositions comprising syndiotactic polypropylene. Examples include Japanese Patent Application 01-152448, Japanese Patent no. JP2824082, U.S. Pat. Nos. 5,476,914, 6,184,326, and 6,245,870 which are directed to vanadium catalysts capable of producing compositions comprising syndiotactic polypropylene having greater than 80% r dyads. However, the crystallinity of the syndiotactic rich polypropylene according to the references prevents the material from being elastomeric. In addition, these references are directed to syndiotactic specific propagation under “catalytic site control”, resulting in “rmmr” segments being present in the polymer produced. This is in contrast to “chain end control” of the present invention, wherein “rrmr” segments are produced and essentially no “rmmr” segments are produced.
U.S. Pat. Nos. 5,326,824, 5,373,059, 5,374,685, and Japanese Patent Nos. JP3025553 are directed to compositions comprising functionalized syndiotactic polypropylene. However, the functionalized syndiotactic polypropylene disclosed in these references has greater than about 50% crystallinity, (e.g., [rrrr]>50%, more preferably [rrrr]>70%), and thus, the polymers so produced are not elastomeric.
The Japanese reference JP2837246 is directed to syndiotactic polypropylene having [rrrr]>80%, an intrinsic viscosity of about 0.01 to 10 dl/g, a Mw/Mn of 1.5 to about 20, a melting temperature Tm of about 130 to 170° C., and a t1/2=2 minutes. The polymers produced according to JP2837246 are thus crystalline, have a melting temperature, and are not elastomeric. In addition, syndiotactic polypropylene produced using vanadium based catalysts result in materials having an ash content, when determined as described herein, of greater than about 1 weight %, due to residual materials from the catalyst being present.
Given the cost and relative viability of polypropylene, there remains a need in the polymer industry for a propylene-based polymer, which has both amorphous and elastomeric character. Such a product would preferably have the novel combination of both high impact strength and high elasticity. In addition, there exists a need for propylene-based polymers, which have crystallinity sufficient to provide function related thereto to an elastomer where an amorphous elastomer may not be suitable for use. In light of the above, it would be desirable to provide a propylene-based olefin which is elastomeric instead of tacky. It would be further desirable for such an elastomer to be produced via an economical process that does not require an exotic catalyst, multiple extractions, multiple processing steps, or other conditions.